The line is that they did not get their paperwork to Spanish Football Federation headquarters until a minute after the 23:00 BST deadline. In their defence, United say they have a receipt that proves they submitted the relevant documents in time.

Real Madrid are likely to appeal to push the transfer through.

United had stood to receive £18.3 million in cash for De Gea, plus Keylor Navas, the Costa Rica No 1, valued at £10.9 million.

The deal — if it went through — would represent a climbdown for United given that they insisted all summer that De Gea would only leave in a straight cash deal worth in excess of the £32.6 million world-record fee that Juventus paid Parma for Gianluigi Buffon in 2001, or as part of a package that brought Sergio Ramos to Old Trafford.

Louis van Gaal, the United manager, had resolved not to select De Gea while the transfer window remained open after claiming that the Spaniard had said he was “not eager to play” against Tottenham Hotspur on the opening day of the season. It was a claim fiercely disputed by De Gea.